A driver assistance system comprises a long-range radar apparatus for the detection of remote objects, especially vehicles travelling ahead, and at least one short-range detection apparatus for the detection of objects in the vehicle's closer proximity. Such assistance systems are now offered by several manufacturers and their scope of performance is being constantly extended.
Current systems detect when a driver approaches a vehicle travelling ahead, determine its speed and, by means of suitable engine, automatic gearbox and/or brake system interventions, maintain a required distance from it with regard to safety aspects. By means of appropriate engine interventions, advanced versions already realize re-acceleration of the vehicle as soon as there is no longer any vehicle travelling ahead in the detection apparatus' range of measurement. In the case of certain commercially available systems, the driver has a possibility of pre-selecting the desired cruising speed and a desired safety distance from vehicles travelling ahead.
To avoid relieving the driver of his responsibility, the chosen amount of deceleration by the aforementioned interventions, and also the chosen amount of acceleration in the event or re-acceleration, are clearly below the value attainable during manual operation of the vehicle, and manual actuation has priority over the assistance system's control functions. The vehicle accelerates in the customary fashion when the accelerator is operated. The pre-selected speed is set again when the driver takes his foot off the accelerator. The assistance system can be deactivated in total by touching the brake pedal or by means of a special operator control of the assistance system.
Although current knowledge of modern driver assistance systems' radar facilities does not hint at any acute health risks, with a view to the increase in electromagnetic pollution they cause and interference with observatories, in some countries there are public authority regulations governing the operating principles of such systems. This includes the requirement that the power radiated by a long-range radar in the current usual frequency band from 76-77 GHz must not exceed a certain value at vehicle standstill. This value lies clearly below the values that are necessary for optimum operation at higher speeds (up to 250 km/h) and current signal processing technologies.
According to the current state of the art, there are diverse approaches towards circumventing or solving this problem. To some extent, manufacturers abstain from delivering their systems to countries where relevant requirements apply. A further possible solution is to use pulsed radar systems in which the pulse pauses are increased when the vehicle is at standstill. The concomitant reduction in verification sensitivity is acceptable at standstill or low speeds but, technically, this system is relatively complex. A further possible solution consists of using a variable-power oscillator or intermediate amplifier or power amplifier. However, this approach also involves considerable complexity and is therefore critical in terms of cost.